Gas turbine compressor system



Ndv. I7, 1953 c PRlcE GAS TURBINE COMPRESSOR SYSTEM 3 Sheets-Sheet 1 Filed Sept. 29, 1948 INVENTOR. NATHAN C. PRICE Ager n Nov. 17, 1953 N. c. PRICE 2,659,528

GAS TURBINE COMPRESSOR SYSTEM Filed Sept. 29, 1948 3 Sheets-Sheet 2 INVENTOR. 5 NATHAN 0. PRICE NOV. 17, 1953 c, P 2,659,528

GAS TURBINE COMPRESSOR SYSTEM Filed Sept. 29, 1948 3 Sheets-Sheet 3 I? n5 I III INVENTOR. NATHAN 0. PRICE AqEn Patented Nov. 17, 1953 GAS TURBINE COMPRESSOR SYSTEM Nathan C. Price, St. Helena, Calif., assignor to Lockheed Aircraft Corporation, Burbank, Calif.

Application September 29, 1948, Serial No. 51,685

11 Claims. (01. 230-114) This invention relates to gas turbine powerplants and relates more particularly to the compressor systems of high pressure gas turbine powerplants intended primarily for the propulsion of aircraft, and the like, the aforesaid compressor systems employing principles of supersonic airflow.

In gas turbine powerplants for the propulsion of aircraft it is necessary, in order to obtain high efficiency, to employ compressors having high compression ratios and the axial flow type of compressor has been found to be satisfactory for this purpose. However, axial flow compressors, more particularly supersonic compressor blading, have rather narrow ranges of stable operation and their efficiency is afiected substantially by variations in altitude, ambient air temperature and the speed of the aircraft. Furthermore, special relationships are to be regarded in connection with the ratio of blading tip speed to the acoustic velocity of the air passing through the blading, affecting blading efficency, and the choice of operation in the supersonic or sub-sonic regime. In high pressure gas turbine engines it is necessary to induct a very great volumetric air flow at the inlet, and to deliver this large mass flow of air, under high pressure and greatly reduced volume, to the combustion chambers and the axial flow compressors are employed in multiple stages or compound relation for this purpose. By employing a plurality of compressors in this manner, it becomes possible to drive the individual compressors at difierent speeds to obtain optimum efficiency. The maximum volumetric flow demand of a compressor system arises at the inlet,

where it is found advantageous to operate blading in the supersonic range. However, this requires the establishment of a comparatively high blade tip speed at the inlet suitably controlled, with respect to conditions of the subsequent compressor blading which, in the invention, is operated at an abruptly lower tip speed, in the subsonic range, to produce a stabilizing region of highly efiicient compression.

It is an object of the present invention to provide a gas turbine powerplant characterized by a multi-stage axial fiow compressor system in which the individual compressors are driven and operated in a manner to obtain high compressor efliciency under the variable conditions of operation. In the system of the invention there are three compressor stages or units, two of the units being driven at a known speed difierential and the third being driven individually in a manner whereby its rotative speed is varied in accordance e. if

with altitude, ambient air temperature and flight speed conditions, said third unit having blading of a different type than the other units, especially suited for high rotative speed operation and capable of increasing the compression ratio and volumetric output of the system. The independent control of the rotative speed of the one stage or unit, which is the foremost or leading unit of the system, corrects or obviates stalling of the earlier blading rows and turbining of the later rows at low rotative speeds and alleviates other phenomena affecting efliciency of the compressor system and of the powerplant as a whole.

Another object of the invention is to provide a powerplant compressor system and drive mechanism of the class referred to wherein the foremost compressor stage is characterized by supersonic blading to afiord a several fold increase of power output. The ultimate power capacity of a gas turbine powerplant depends upon the quantity of air which it can induct. This induction reaches a maximum when supersonic blading is used at the engine air inlet, which permits inflow at approximately the velocity of sound. However, supersonic blading has extremely sharp characteristics, and it is desired to carry the remainder of the compression following thereafter in blading of the sub-sonic type, having broader and more easily controllable characteristics. The transition of flow from the supersonic to the sub-sonic blading involves a sharp discontinuity in operating conditions which is satisfactorily compensated for by the construction described hereinafter.

A further object of the invention is to provide a compressor system of the class described wherein the supersonic compressor is driven directly from the turbine shaft assembly through a variable speed hydraulic drive and is not associated structurally with the drive for the second stage compressor.

It is also an object of the invention to provide a compressor system which can be contained within a generally cylindrical casing, having a row of supersonic compressor blading of very high tip speed at the inlet, followed by sub-sonic blading of abruptly lower tip speed, including a construction for a portion of this sub-sonic blading adjacent to the compressor system outlet to be operated at a partially elevated tip speed, to maintain a more or less constant Mach number in all of the sub-sonic compressor blading, preferably a Mach number of between .7 and .8 for best efiiciency.

Other objectives and advantages of the inven- 3 tion will become apparent from the following detailed description, throughout which reference is made to the accompanying drawings wherein:

Figure l is a side elevation of a powerplant embodying the features of the present invention, with the principal elements appearing in broken lines;

Figure 2 is an enlarged elevational view of the forward portion of the powerplant with the upper part appearing in longitudinal cross section and illustrating one form of control in a diagrammatic manner;

Figure 3 is an enlarged fragmentary vertical detailed sectional view illustrating the hydraulic drive for the supersonic compressor blading and adjacent parts;

Figure 4 is a view taken substantially as indi-. cated by line 4-4 on Figure 2 illustrating the character of the guide vanes and supersonic blad- Figure 5 is an enlarged developed or schematic view of the forward blading rows of the compressor system taken substantially as indicated by line 55 on Figure 2 and Figure 6 is a schematic view illustrating another form of control for the supersonic compressor.

The powerplant illustrated in Figure 1 and which incorporates the features of the invention includes an elongate sectional housing or casing H). The forward major portion of the casing l5 contains the compressor system of the invention while the rear portion of the casing houses the combustion chamber II and turbine |2. The turbine |2 discharges the turbine gases through the tail pipe portion l3 in the form of a propulsive jet. The forward end of the casing I0 is open to form a ram inlet l4 of large volumetric flow capacity for the compressor system. The combustion chamber H, which may be annular, is supplied with fuel and the compressor system discharges the continuous large mass flow of greatly reduced volume of compressed air into the chamber. The resultant hot combustion gases and air are discharged from the combustion chamber under pressure through a nozzle ring L3 to drive the turbine l2. The turbine l2 in turn drives the compressor system in the manner hereinafter described.

The compressor system of the invention includes a rear or third stage compressor I5, an intermediate or second stage compressor I1, and a front or first stage compressor IS.

The rear, or third stage compressor l5, comprises a tubular and generally cylindrical housing 20 spaced within the intermediate portion of the powerplant casing I0 and a rotor 2| operating within the housing. The housing 2|] carries a plurality of rows of inwardly projecting stator blades 22 and the rotor 2|, which is of rearwardly increasing diameter, carries a plurality of rows of outwardly projecting impeller blades 23 operating between the rows of stator blades. The rotor 2| of the rear compressor I6 is driven directly by the rotor of the turbine l2 and the compressor and turbine rotors may be so constructed as to constitute a single composite rotor assembly. Ducts 8 deliver or direct the compressed air from the intermediate compressor I! to the forward end of the housing 213 of the third stage compressor.

The intermediate compressor I1 is arranged ahead of the compressor l6 and includes a hollow or tubular rotor shell 24 of rearwardly increasing diameter. The rotor shell 24 'is arranged concentrically within the casing l0 and carries a plurality of rows or stages of outwardly projecting rotor blades 25. The rows of blades 25 operate between rows of stator blades 26 which project inwardly from the wall of the casing H3. The blades 22, 23, 25 and 26 of the compressors l5 and I! are of the sub-sonic type. The rotor shell 24 of the compressor I! has a forward hub plate 21 and a rear hub plate 28. A suitable bearing 29 supports the forward hub plate 21 on the tubular central portion of a stationary web 30. The web 30 is in turn carried by a row of stationary diffuser blades 3| arranged ahead of the foremost row of rotor or impeller blades 25. The outer ends of the blades 3| are suitably secured and supported in the casing H). The rear hub plate 28 of the rotor 24 is mounted on a stationary generally tubular support member 32 through an appropriate bearing 33.

As above described, the rotor 2| of the rear compressor H5 is connected or associated with the turbine rotor to be directly driven thereby.

, In accordance with the invention a speed reducing drive is provided between the compressors I5 and H, the drive being from the rotor 2| of the compressor I6 to the rotor 24 of the compressor IT. This drive mechanism includes the above mentioned stationary tubular member 32 and two spaced stationary diaphragms or plates 34 and 35 secured to or formed on spaced radial blocks 35 secured in the wall of the casing In. As illustrated in the drawings, the casing l0 may be split or divided at the radial blocks 31 to facilitate assembly and the sections of the casing may be secured together by screws or bolts 31. A beveled drive gear 38 surrounds the rear portion of the stationary member 32 and is driven by the forward hub portion of the compressor rotor 2| through end splines or curvic splines 39. A thrust bearing 40, carried by the plate 35, supports the gear 38. Sets of radially disposed cluster pinions 4| and 42 are arranged between the spaced plates 34 and 35. Appropriate bearings 43 support the inner pinions on the member 32 so as to mesh with the drive gear 38. The outer pinions 42-, which are connected with the inner pinions 4| by end splines and screws 44, are supported on the plates 34 and 35 by bearings 45. A driven gear 46, of relatively large diameter, meshes with the pinions 42 to be driven thereby and is supported by bearing means 41 on the stationary plate 34. The driven gear 46 is connected with the hub plate 28 of the rotor shell 24 by flexible cushion splines 48. It will be seen that with the structure just described, the rotor 24 of the compressor H is driven by the rotor 2 of the compressor H5 at a slower rotative speed than the rotor 2|. In a representative case, the blading tip diameter of the compressor I1 is 92% greater than that of the compressor l6 but the rotative speed of compressor i-l is 43% that of the compressor l5, whereby the blading of the two compressors differs only in scale, and it becomes possible to operate the blading of both compressors at similar blade angles and approximately the same relative Mach numbers to attain high efliciency.

This similarity, except for scale, also leads to a reduced manufacturing cost in various ways.

In a typical engine of the invention the rated speed of the rear compressor rotor 2| may be 16,800 R. P. M. with a blading tip speed of 925 ft. per second, while the rated speed of the intermediate compressor rotor 24 may be 7,200 B. P. M. with a blading tip speed of 760 ft. per

second, it being apparent that the ratio of the speed reduction drive may be varied in different engines, taking into account the change of acoustic velocity of the entrained air, as a result of changing air temperature at various portions of the compressor system, to maintain a substantially constant Mach number in the sub-sonic compressor blading. However, the first stage compressor I8 is revolved up to a speed of 16,500 R. P. M. at times, producing a blade tip speed of 1,750 ft. per second, being well within the supersonic range of compression. A relative velocity of the blading against the air is thereby brought to a value between 1.5 and 2.00 times the velocity of sound at certain times.

The forward end or ram inlet [4 of the casing I is preferably equipped with an inlet spider comprising a hub 50 and a set or row of guide vanes 5|. The spider is stationary, the vanes 5| being suitably secured in the forward end of I the casing 10. The vanes 5| extend radially inward from the wall of the casing I8 and are airfoil shaped in cross section as shown in Figure 5. The vanes 5|, in addition to supporting the hub 58, serve to impart an initial swirl or rotation to the ram air entering the compressor system, being set at an angle of incidence relative to the axis of the casing II] to guide or direct the entering air in this manner. Adjacent to the hub 50 the guide vanes 5| are set to cause the entering air to swirl or rotate in a direction counter to the direction of rotation of the blades of the first stage compressor Is to increase the efficiency cf the compressor but adjacent to the casing I8 the guide vanes cause the inducted air to swirl The first or front compressor |8 comprises a rotor 53 arranged between the stationary supporting web 38 and the stationary hub 50 of the inlet spider, to be ahead of or upstream from the rotor 24 of the compressor l1. the rotor 53 may be a solid disc like member provided at its forward end with a hub part 54 of reduced external diameter which extends into the stationary inlet hub 58. A bearing 55, having an associated seal 56, mounts the part 54 in the hub 58 to support the rotor 53 for free rotation. The periphery of the rotor 53 is substantially flush with the peripheries of the rotor 24 and inlet spider hub 50 and carries a row of supersonic compressor blades 51. The direction of rotation of the supersonic blades 51 is indicated by the arrow X in Figure 5, where it will be seen that the blades 51 are of triangular cross section, each having a plain flat leading face and a trailing side defined by two substantially fiat faces 53 and 59 joining at an apex edge 68. As will be seen from an inspection of Figure 5, the supersonic blades 51 have a substantial pitch and, as shown in Figure 4, the blades 51 have a partial solidity, being in axially overlapping relation for some distance outwardly from their roots. In the operation of the powerplant the axial motion of the ram air reaches or approaches the velocity of sound in a plane slightly ahead of the supersonic blades 51. The blades If desired,

51, of triangular configuration, eliminate or reduce the propagation of heavy rearwardly traveling shock waves which might otherwise be developed where the velocities are of sonic or supersonic values. In operation, a comparatively gentle initial oblique shock wave (1 extends from the leading edge of one blade 51 toward the leading edge of the adjacent blade 51 where it sets up interference with or joins other shock waves propagated between the leading edge and the apex line 60, so that heavy waves are avoided in this region. One or more light oblique shock waves such as b and 0 may be generated prior to the normal wave d thereby approaching adiabatic compression of the air. The employment of the supersonic blades 51 greatly increases the volumetric capacity and raises the compression ratio of the compressor system.

The abovementioned stationary diffuser blades 3| stand between the row of supersonic blades 51 and the first row of sub-sonic blades of the compressor H, as shown in Figure 5. The row of diffuser blades 3| is shaped to change the direction of flow of the air leaving the supersonic blades 51 to direct it to the blades 25 for the efiicient compression of the air. The direction of rotation of the sub-sonic rotor blades 25 is indicated by the arrow Y.

In accordance with the invention the rotor 53 of the compressor |8 is driven by the turbine |2 through a variable speed drive so that the rotational speed of the rotor 53 may be varied in accordance with or to compensate for variations in altitude, ambient air temperature, etc.

The invention in its broader aspects may utilize any appropriate form or type of variable speed drive for the supersonic compressor rotor 53. In an illustrative case, the rotative speed of rotor 53 will be variable, depending on ambient conditions, up to a speed of 98% of the turbine rotor speed. In the particular embodiment of the invention illustrated, a variable speed by draulic coupling of the type described in United States Letters Patent No. 2,448,825, granted to me September '7, 1948, is employed to drive the rotor 53. A shaft 98 is splined to the forward hub of the rear compressor rotor 2| at 6| and extends forwardly to drive the hydraulic mechanism. The rotor or drive element 62 of the hydraulic drive may be an annular part splined to the forward end of the shaft 98 and substantially received in an annular recess 63 in the rear face of the rotor 53 of the supersonic compressor I8. A cover plate or ring 64 is held in the recess 63 by a snap-ring 9, or the equivalent, and extends inwardly across the rear side of the driver element 62. A fioating ring 65 is arranged in the plate 64 outwardly of the driver element 62. The ring 65 may rotate with the driver element 62 but is free for at least limited angular movement relative to the element 62.

The wall of the abovementioned recess 63 has an annular depression or groove 66 concentric with the axis of rotation of the rotor 53 and the opposing surfaces of the driving element 62 and ring 65 have a complementary groove 61 which, together with the groove 66, forms a chamber. Vanes 68 are provided on the wall of the groove 66 and shafts or shanks 69 carried in axial grooves in the driver element 62 support vanes 18 within the groove 61. The shanks 69 are adapted to be turned or rotated to vary the angle of the vanes 10. The floating ring 65 and the vane shanks 69 have meshing splines or teeth 12 so that the ring serves to maintain the several vanes III in the same an ular p sit on w en the drive is idle, etc.

Means is provided for vary n the angle of the vanes III associated with the driver element 82. This means includes a radial cylinder I3 formed in the driver element adjacent each vane shank 89. Pistons or plungers I4 operate in the cylinder bores 18 and cooperate with cam .faces 15 on the shanks 59 of the vanes I0. An annular groove I8 in the driver element 82 is supplied with liquid under pressure by a port system I! extending through the shaft 98 and radial ports I8 connect the inner ends of the cylinders I3. with the grooves I6. It will be seen that by varying the pressure on the liquid supplied to the cylinders 13 the angle oi the series of vanes I8; may be changed to control or vary the transmission of torque through the hydraulic coupling.

The chamber defined by the grooves 88 and 61 contains a liquid which may be replenished by leakage from the cylinders 13 together with any additional circulation if required, from another flow source. A return port 80 leads through the driver element 62 past the bearing 8| which mounts the element in the stationary web 30. The liquid lubricates the bearing 81 and passes therethrough into a reservoir 83 housed in the rotor shell 24. Suitable seals 82 at the web 3|] and reservoir 83 prevent the leakage of liquid iron; the hydraulic mechanism and from the reservoir.

The compressor system of the invention includes a control means for regulating the speed of the supersonic blades 51. Figure 2 of the drawings illustrates in a diagrammatic manner one representative form of such a control means which includes an evacuated bellows 9| housed with a capsule 98. In the particular case illustrated, the capsule 96 is stationarily associated with the stationary reservoir 83, it being understood that the capsule may be supported in other positions. The capsule 96 is closed or sealed except for a line or duct system which maintains the interior of the capsule in communication with the outlet region of the second stage compressor II. In the diagrammatic illustration of Figure 2, this duct system includes a line and port system I08 leading from the interior of the capsule 96 through the shaft 98 to the interior of the rotor 2| where it has communication with the come a pressor duct 8. The air pressure at the outlet of the compressor I1 is continuously supplied to the interior of the capsule 98, by the port system I00 to act upon the evacuated bellows 91.

The control means for regulating the speedof the supersonic blading 51 further includes a pump 85 driven by the shaft 98 and drawing oil, or the like, from the reservoir 83 to supply it under pressure to a tube 94 leading to the abovementioned port system '11. The pressure in the port system I1 and therefore the pressure applied to the plungers I4 of the hydraulic drive is regulated by a needle 93 which is movable to vary the opening in a bleed port 91 in the wall of the tube 94. The bleed port 91 may discharge directly into the reservoir 83. The needle 93 is attached to the free end of the bellows 9| to be moved in response to variations in the, Outlet pressure of the compressor II. Therefore, when a predetermined air pressure is attained at the discharge, of the second stage compressor II, the resultant deflection of the bellows 9| draws the needle 93 from the port 91, reducing or limiting the pressure applied to the plungers I4 thereby adjusting the speed of rotation of the supersonic blading 5,1 to establish a given pressure at the outlet, of the, compressor [1. It will be apparent how the control means just described serves to automatically regulate the hydraulic drive for the row of supersonic blades Bl to preserve an eflicient, stabilized condition in the compressor system.

Figure 6 illustrates another representative form of control means for the hydraulic drive of the supersonic compressor I6. In this case, the needle 9,3, controlling the bleed port 91 of the tube 94, is secured to a flexible diaphragm H0. The diaphragm H0 divides the interior of a sealed capsule into two chambers III and H2. The diaphragm H0 and the needle 93 are urged toward the port 91 by a compression spring H3. A tube or duct I I4 leads from the chamber I I2 to a port or pressure tap H5 in the wall of the casing I0 and a similar duct H6 leads from the chamber III to a pressure tap H1 in the wall of the easing. The pressure taps H5 and III are located very slightly downstream from the opposite margins of the average normal cross sectional region of the normal shock wave at the supersonic blading 51. With this arrangement the pressure at the tap I I5 is applied to one side of the diaphragm H0 to urge the needle 93 toward an open position while the pressure at the tap H1 is applied to the other side of the diaphragm to urge the needle 93 toward the closed position. In the operation of this form of control the rotative speed of the row of supersonic blading 51 is automatically maintained at a value at which the average region of the normal shock wave is bordering the edge of or just passing over the pressure tap I II. In the event the speed of the row of blades 5! increases to the extent that the region of the normal shock wave passes beyond the tap III the pressure in the chamber III is reduced so that the pressure in the chamber I I2 moves the needle 93 outwardly. This reduces or limits pressure applied to the plungers I4 so that less torque is transmitted to the hydraulic drive and the speed of the blades 51 is thus reduced. In the event the speed of the blades 51 is reduced below the proper value, the reduced differential in pressures in the chambers III and H2 permits the needle 98 to move toward the closed position under the action of the spring H3 thus increasing the pressure applied to the plunger I4 to increase the torque transmitted to the blading row 51, bringing the speed of the supersonic compressor up to the correct value.

Having described only typical forms of the invention I do not wish to be limited to the specific details herein set forth, but wish to reserve to myself any variations or modifications that may appear to those skilled in the art and fall within the scope oi the following claims.

I claim:

1 A compressor system for a turbo power-plant having a turbine rotor element, said system comprising a final stage compressor driven by said element and supplying compressed air to the powerplant, an intermediate stage compressor delivering compressed air to the final stage compressor, a speed reducing drive connecting the intermediate stage compressor with the final stage compressor to be driven thereby, a first stage compressor ahead of the intermediate stage compressor for delivering compressed air thereto, the first stage compressor being characterized by supersonic blading, and a variable speed drive, connecting the first stage compressor with the final. stagecompressor to be driven thereby.

2. A compressor system for a turbo powerplant having a rotating turbine element, said system comprising first, second and third stage axial flow compressors arranged in compounded relation and supplying compressed air to the powerplant, a drive connecting said turbine element and a third stage compressor whereby the third stage compressor has a rotational speed substantially the same as the turbine element, a speed reduction drive connecting the second and third stage compressors whereby the second stage compressor is driven at a slower rotational speed than the third stage compressor, and a variable speed drive mechanism connecting the first stage compressor with the third stage compressor.

3. A compressor system comprising at least three rows of compressor blading arranged in compound relation, a gear box connecting the discharge and intermediate rows, and a power source connected with the inlet row to drive the same at a Mach number exceeding 1.0 and connected with the outlet row to drive the intermediate and outlet rows at Mach numbers between 0.7 and 0.8, the diameter of the intermediate blading row being substantially greater than that of the outlet row.

4. A compressor system for a gas turbine powerplant comprising first, second and third stage axial fiow compressors arranged in series relation, a direct drive between the turbine and third stage compressor, a speed reducing gear drive between the third and second stage cornpressors for driving the second stage compressor at a slower speed than the third stage compressor, the gear drive comprising a driving gear associated with the third stage compressor, a driven gear associated with the second stage compressor, a stationary structure having an axial opening therethrough, and sets of radially disposed cluster pinions carried by said structure and meshing with said gears, and a shaft connected with. the third stage compressor to be driven by the turbine and passing through said opening and connected with the first stage compressor to drive the first stage compressor.

5. A compressor system for a gas turbine including a casing, a series of compressors in the casing, the first compressor of said series including a rotor, and supersonic blading on the rotor, means for transmitting power from the turbine to the compressors to drive the same including a shaft rotated by power from the turbine, a hydraulic coupling connecting the shaft with said rotor including a fluid pressure actuated means operable to vary the speed of the rotor, a control for said fluid pressure actuated means comprising a device for varying the application of fluid pressure to said means, a diaphragm for operating said device, two pressure taps in the wall of the casing adjacent the opposite margins of the region of the normal shock wave at the tip path of said blading, and ducts leading from said taps to the opposite sides of the diaphragm.

6. In a gas turbine power plant having a turbine rotor; the combination of a first stage compressor including a rotor and supersonic blading on the rotor, a second stage compressor downstream from the first stage compressor, a third stage compressor downstream from the second stage compressor and including a rotor connected with the turbine rotor to rotate therewith, a speed reducing drive connecting the second stage compressor with the rotor of the third stage compressor for driving the second stage compressor at a slower rotational speed than the third stage compressor, and a variable speed drive connecting the rotor of the first stage compressor with the rotor of the third stage compressor to drive the first stage compressor, said turbine rotor providing the power for operating said three compressors.

7. In a power plant having a power-providing turbine rotor; a compressor system for the power plant comprising first, second and third stage axial flow compressors arranged in compounded relation and supplying compressed air to the power plant, the third stage compressor including a rotor attached to the turbine rotor so as to therewith constitute a composite rotor assembly, a speed reduction drive connecting the second stage compressor with said rotor assembly whereby the second stage compressor is driven at a slower rotational speed than said rotor assembly, and a variable speed drive mechanism connecting the first stage compressor with said composite rotor assembly whereb the first stage compressor is driven by said roto-r assembly, the first stage compressor being of the supersonic type, and the second and third stage compressors being of the sub-sonic type.

8. A compressor system for a gas turbine power plant having a power producing turbine rotor, said system comprising first and second stage compressors arranged in serial relation, a cylindrical casing for the compressors, a driving member directly connected with the turbine rotor to rotate therewith, a gear drive connecting the member and the second stage compressor for driving the latter at sub-sonic velocities, and a variable speed drive connecting the first stage compressor with the driving member for driving the first stage compressor at supersonic velocities.

9. A compressor system for a turbo powerplant having a turbine comprising the combination of a series of first, second and third stage axial flow compressors, the first of said series being a supersonic compressor and the other compressors of the series being of the sub-sonic type; means connecting the third stage compressor with the turbine to be driven thereby; a shaft driven by the third stage compressor; a variable speed coupling connecting said first stage compressor with the shaft to be driven thereby, the coupling including fluid pressure actuated means operable to vary the speed of rotation of said first stage compressor; a control device in communication with said pressure actuated means operable in response to varying air pressures to supply variable fluid pressure to said pressure actuated means; duct means maintaining said device in communication with a region of said series of compressors downstream from said first stage compressor to operate said control device and thus vary the speed of said first stage compressor, and drive means operativel connecting the second stage compressor with the third stage compressor to be driven thereby.

10. A compressor system for a turbo powerplant having a turbine, said system including a series of axial fiow compressors, the first of said series being a supersonic compressor and the other compressors of the series being of the subsonic type; means operatively connecting the third stage compressor with the turbine to be driven thereby; a shaft driven by the third stage compressor; a variable speed hydraulic coupling connecting said shaft with said first compressor, said coupling including fluid pressure actuated means operable to vary the speed of said first compressor; means for supplying actuating fluid pressure to said pressure actuated means of the coupling; an air pressure actuated device for varying the application of said actuating fluid pressure to said pressure actuated means and thus vary the speed of said first compressor; means for conducting air pressure from said series of compressors to said device to actuate 'the same; and means operatively connecting the second stage compressor with the third stage compressor to be driven thereby.

11. A compressor system for a gas turbine including a casing, a series of compressors in the casing, the first compressor of said series including a rotor, and supersonic blading on the rotor, means for transmitting power from the turbine to the compressors to drive the same including a shaft rotated by power from the turbine, a hydraulic coupling connecting the shaft and said rotor including a fluid pressure actuated means operable to vary the speed of the rotor, a control for said fluid pressure actuated means comprising a device for varying the application of fluid pressure to said means, air pressure actuated means operatively connected with said device,

12 andducts communicating with the recioxrot the normal shock wave in the casing adjacent the tip path ofisaid blading .to receive air pressure from said region and communicating with said. air;pressure actuated means to supply air pressure thereto to operate the same.

NATHAN C. PRICE.

References Cited in theme of this patent UNITED STATES PATENTS Number Name Date 1,947,477 L'ysholm -.es Feb. 20, 1934 2,283,434 Haliord et'al. May 19, 1942 2,346,032 'Kinnuean e Apr-.4, 1944 2,405,723 Way Aug. 13, 1946 2,409,176 Allen Oct. 15, 1916 2,435,236 Bedding Feb. '3, 1948 2,461,931 Smith "et'al. Feb. 15,1949 2,528,635 Bell et a1. Nov. 7, 1950 FOREIGN PATENTS Number Country Date 505,829 Great Britain May 17, 1939 

